1. Field of Invention
This invention relates to novel and improved reversible drive apparatus for a flexible web such as an inking ribbon in a printing machine. The reversible drive apparatus is characterized by its simplicity, low cost and ease of manufacture.
In printing machines using inking ribbons, it is conventional to provide a ribbon drive device to advance the ribbon after the printing of one or more characters. Advancement of the ribbon greatly enhances the clarity of the printed characters. In general, the ribbon is drawn from a supply spool to a take-up spool until the supply spool is fully unwound. Then the direction of ribbon feed is reversed whereby the original take-up spool now becomes the supply spool and the original supply spool becomes the take-up spool. This periodic reversal of the direction of ribbon feed greatly increases the useful like of the ribbon.
2. Prior Art
There have been many prior art attempts to achieve ribbon motion reversal by shifting a driving gear (driven by a single motor or driving force) between individual gear trains associated with the two ribbon spools. Typical prior art reversing mechanisms of this type are disclosed in U.S. Patent Nos. 1,309,423 and 3,670,981. These prior art ribbon reversing mechanisms generally use mechanical linkages which are rather complex, costly and unreliable. As a result, many printing machines have been designed to use two motors, one for each spool, and a motor control circuit which alternately drives the motors.